Vehicle security systems are widely used to deter vehicle theft, prevent theft of valuables from a vehicle, deter vandalism, and to protect vehicle owners and occupants. A typical automobile security system, for example, includes a central processor or controller connected to a plurality of vehicle sensors. The sensors, for example, may detect opening of the trunk, hood, doors, windows, and also movement of the vehicle or within the vehicle. Ultrasonic and microwave motion detectors, vibration sensors, sound discriminators, differential pressure sensors, and switches may be used as sensors. In addition, radar sensors may be used to monitor the area proximate the vehicle.
The controller typically operates to give an alarm indication in the event of triggering of a vehicle sensor. The alarm indication may typically be a flashing of the lights and/or the sounding of the vehicle horn or a siren. In addition, the vehicle fuel supply and/or ignition power may be selectively disabled based upon an alarm condition.
A typical security system also includes a receiver associated with the controller that cooperates with one or more remote transmitters typically carried by the user as disclosed, for example, in U.S. Pat. No. 4,383,242 to Sassover et al. and U.S. Pat. No. 5,146,215 to Drori. The remote transmitter may be used to arm and disarm the vehicle security system or provide other remote control features from a predetermined range away from the vehicle. Also related to remote control of a vehicle function U.S. Pat. No. 5,252,966 to Lambropoulous et al. discloses a remote keyless entry system for a vehicle. The keyless entry system permits the user to remotely open the vehicle doors or open the vehicle trunk using a small handheld transmitter.
Unfortunately, the majority of vehicle security systems need to be directly connected by wires to individual vehicle devices, such as the vehicle horn or door switches of the vehicle. In other words, a conventional vehicle security system is hard-wired to various vehicle components, typically by splicing into vehicle wiring harnesses or via interposing T-harnesses and connectors. The number of electrical devices in a vehicle has increased so that the size and complexity of wiring harnesses has also increased. For example, the steering wheel may include horn switches, an airbag, turn-signal and headlight switches, wiper controls, cruise control switches, ignition wiring, an emergency flasher switch, and/or radio controls. Likewise, a door of a vehicle, for example, may include window controls, locks, outside mirror switches, and/or door-panel light switches.
In response to the increased wiring complexity and costs, vehicle manufacturers have begun attempts to reduce the amount of wiring within vehicles to reduce weight, reduce wire routing problems, decrease costs, and reduce complications that may arise when troubleshooting the electrical system. For example, some manufacturers have adopted multiplexing schemes to reduce cables to three or four wires and to simplify the exchange of data among the various onboard electronic systems as disclosed, for example, in “The Thick and Thin of Car Cabling” by Thompson appearing in the IEEE Spectrum, February 1996, pp. 42-45.
Implementing multiplexing concepts in vehicles in a cost-effective and reliable manner may not be easy. Successful implementation, for example, may require the development of low or error-free communications in what can be harsh vehicle environments. With multiplexing technology, the various electronic modules or devices may be linked by a single signal wire in a bus also containing a power wire, and one or more ground wires. Digital messages are communicated to all modules over the data communications bus. Each message may have one or more addresses associated with it so that the devices can recognize which messages to ignore and which messages to respond to or read.
The Thompson article describes a number of multiplexed networks for vehicles. In particular, the Grand Cherokee made by Chrysler is described as having five multiplex nodes or controllers: the engine controller, the temperature controller, the airbag controller, the theft alarm, and the overhead console. Other nodes for different vehicles may include a transmission controller, a trip computer, an instrument cluster controller, an antilock braking controller, an active suspension controller, and a body controller for devices in the passenger compartment.
A number of patent references are also directed to digital or multiplex communications networks or circuits, such as may be used in a vehicle. For example, U.S. Pat. No. 4,538,262 Sinniger et al. discloses a multiplex bus system including a master control unit and a plurality of receiver-transmitter units connected thereto. Similarly, U.S. Pat. No. 4,055,772 to Leung discloses a power bus in a vehicle controlled by a low current digitally coded communications system. Other references disclosing various vehicle multiplex control systems include, for example, U.S. Pat. No. 4,760,275 to Sato et al.; U.S. Pat. No. 4,697,092 to Roggendorf et al.; and U.S. Pat. No. 4,792,783 to Burgess et al.
Several standards have been proposed for vehicle multiplex networks including, for example, the Society of Automotive Engineers “Surface Vehicle Standard, Class B Data Communications Network Interface”, SAE J1850, July 1995. Another report by the SAE is the “Surface Vehicle Information Report, Chrysler Sensor and Control (CSC) Bus Multiplexing Network for Class ‘A’ Applications”, SAE J2058, July 1990. Many other networks are also being implemented or proposed for communications between vehicle devices and nodes or controllers.
In addition to vehicle security and remote keyless entry functions, another type of desirable vehicle remote control function is remotely starting the vehicle engine when the owner is away from the vehicle. Such remote starting can be used in cold climates to warm the engine and/or run the passenger compartment heater, to thereby prevent freezing or for the user's comfort. Conversely, remote engine starting can enable the air conditioning to run to cool the vehicle's interior before the vehicle user enters the vehicle.
Unfortunately, conventional vehicle control systems, such as aftermarket remote engine starting systems, are for hard-wired connection to vehicle devices and are not readily adaptable to a vehicle including a data communications bus. Moreover, remote starting of the engine presents additional difficulties compared to some other vehicle control applications. This is so because starting the engine may require certain vehicle conditions are correct prior to starting the engine and while the engine is running with the vehicle unattended. It may also be necessary for a remote starter system to bypass an immobilizer device which is part of the security system of some vehicles. For example, U.S. Pat. No. 5,612,578 to Drew entitled “Vehicle Engine Start Control Apparatus Including Interface Device Facilitating Installation and Related Methods” discloses a remote start system which is hard-wire connected via mating plugs for more conveniently bypassing an immobilizer circuit based upon a coded resistance of the ignition key.
A remote starter system may also desirably be able to interface with one or more vehicle controllers, such as for engine management and transmission control, for example. In addition, a remote starter system, even if it were adapted for a communications bus and devices for one particular model, model year, and manufacturer, may not be compatible with any other models, model years, or manufacturers.
One particularly difficult condition to sense for remote starting is vehicle engine speed or RPM. For a typical hard-wired remote start system, an electrical connection is made to obtain a tachometer signal, such as by tapping to the high voltage ignition system, or to vehicle fuel injector system. Such a connection or interface can be relatively difficult and add additional cost to the remote starter, while also reducing its potential reliability.